Sulphur cement generally refers to a product comprising at least sulphur and a filler. To improve the properties of the sulphur cement, the sulphur may be modified using a sulphur modifier, e.g. naphthalene or olefinic compounds such as 5 ethylidene-2-norbornene (ENB) or 5 vinyl-2-norbornene (VNB), dicyclopentadiene, limonene or styrene. Usual sulphur cement fillers are particulate inorganic materials.
Sulphur cement-aggregate composites generally refer to a composite comprising both sulphur cement and aggregate. Examples of sulphur cement-aggregate composites are sulphur mortar, sulphur concrete and sulphur-extended asphalt.
It is known to use organosilane compounds as a stabilising agent in sulphur cement or sulphur cement-aggregate compositions to improve water stability. In U.S. Pat. No. 4,164,428 for example, a modified sulphur composition (often referred to as plasticized sulphur composition) comprising at least 50% by weight of sulphur, a sulphur modifier (often referred to as sulphur plasticizer), a finely divided particulate mineral suspending agent, and an organosilane stabilising agent is disclosed. It is mentioned that suitable organosilanes have the general molecular formula R—Si(OR′)3, wherein R′ is a low molecular weight alkyl group and R is an organic radical having at least one functional group, usually bonded to the silicon atom by a short alkyl chain. Gamma-mercaptopropyltrimethoxysilane is mentioned as a preferred organosilane.
In U.S. Pat. No. 4,376,830 a sulphur cement-aggregate composition comprising a sulphur cement and an aggregate containing an expansive clay and processes for preparing such compositions are disclosed. The processes, and resulting compositions, are characterised by the addition of certain organosilane compounds in the composition prior to solidifying (cooling) the composition. It is mentioned that suitable organosilanes have the formula Z—Si(R1R2R3), wherein R1, R2 and R3 may be lower alkoxy groups and Z is an organic radical attached to Si via a carbon atom and has at least one molten-sulphur reactive group. Z may for example be mercaptoalkyl. Gamma-mercaptopropyltrimethoxysilane is mentioned as a preferred organosilane.
In WO 2007/65920, sulphur cement or a sulphur cement-aggregate composite is prepared by admixing an inorganic filler and a polysulphide-containing organosilane, mixing with molten sulphur and solidifying the admixture. This process provides sulphur cement or a sulphur cement-aggregate composite with lower water uptake. A preferred polysulphide-containing organosilane is bis(3-triethyoxysilylpropyl)tetrasulphide.
In WO 2008/148804, a sulphur cement pre-composition is prepared by mixing sulphur with a polysulphide-containing organosilane. The sulphur cement pre-composition can be mixed with particulate inorganic material to provide a sulphur cement product. The sulphur cement products have improved water uptake behaviour. A preferred polysulphide-containing organosilane is bis(3-triethyoxysilylpropyl)tetrasulphide.
The polysulphide-containing organosilanes can be used to provide sulphur cement products with low water uptake. However, these organosilanes are expensive and it would be desirable to use less expensive organosilane coupling agents and to have a greater choice of organosilane coupling agents. Additionally it is desirable to avoid the use of organosilanes such as Gamma mercaptopropyltrimethoxysilane, which has an unpleasant smell and has to be handled with care (dissociation of hydrogen from the organosilane can lead to hydrogen sulphide evolution upon contact with sulphur). The present inventors have sought to provide alternative methods for preparing sulphur cement products, whilst retaining low water uptake properties.